Slides in this set

Slide 1

Slide 2

Single-celled organismsThey have just a single cell-surface membrane.This means diffusion can take place quickly and easily. Some have a cell wall, but it is completelypermeable and does not affect diffusion at all. This means that they do not need any specialised gas-exchange surface.…read more

Slide 3

InsectsThey are terrestrial organisms and so water evaporation can be a problem. Therefore they have a special system called tracheae. This is a network of tubes which branch off into tracheoles.They extend to the tissues, and so they take oxygen to the tissues and take carbon dioxide away from the tissues. A steep concentration gradient is maintained within them. They have spiracles which are the ends of the tracheoles that can be opened and closed to prevent water loss. They move muscles in their bodies in order to ventilate.…read more

Slide 4

FishFish have an impermeable body, so they exchange gas through their gills. The gills are located behind the head of the fish. They are made from gill filament, which are like stacked piles. The gill lamella lies at a right angle to the filament. Fish take in water through their mouth and force it over their gills. Theyremove the oxygen from the water via diffusion and the water leaves the fish via the slits in the sides of their head.The oxygen diffuses into the blood via concurrent flow, which allows for a constant diffusion gradient to be maintained.Concurrent flow is where the blood flows in the opposite direction to thewater, and so there is always more oxygen in the water than in the blood, so diffusion continues.…read more

Slide 5

PlantsCarbon dioxide is needed for photosynthesis and produced in respiration. Oxygen is needed for respiration and produced in photosynthesis. However gas exchange is still needed because the products of each reaction are not always enough. Plants are very thin, so a lot of oxygen and carbon dioxide can diffuse straight in.They also have pores called stomata, which open and close to allow gases in and out.Opening the stomata can lead to water loss, so the plants will only open them occasionally. They have a lot of air spaces to allow gases in and out easily.…read more

Slide 6

Mammals Mammals have a small surface area to volume ratio, so they need a specialised surface.They have lungs which have a large surface area to volume ratio through tiny alveoli.The diffusion pathway is also very thin to allow quick diffusion of gases. The lungs also have movement of the internal and external medium which maintains a concentration gradient.The lungs are located inside their bodies to prevent evaporation by water loss.…read more